Uruks AppearUruks Appear - The first Uruk-hai of Middle Earth were not bred by Saruman, but by Sauron centuries earlier.  Treebeard speculates that Uruks are a hybrid of Orcs and Men.

 

"He has taken up with foul folk, with the Orcs.  Brm, hoom!  Worse than that; he has been doing something to them; something dangerous.  For those Isengarders are more like wicked Men.  It is a mark of evil things that came in the Great Darkness that they cannot abide the Sun; but Saruman's Orcs can endure it, even if they hate it.  I wonder what he has done?  Are they Men he had ruined, or has he blended the races of Orcs and Men?  That would be a black evil!" ~The Two Towers, Book III, chap. 4 (Treebeard)